1. Field of the Invention
The present invention relates broadly the wheel alignment for vehicles, and more particularly to tapered shim elements configured to be secured together into a shim assembly which can be positioned as a single, unitary component to alter and correct the relative position of an axle or spindle and, ultimately, of a wheel carried on such axle or spindle.
2. Related Art
The concept of utilizing one or more thin, identical tapered shim elements interposed substantially perpendicular to the axis of an axle or spindle is old and well developed. Much effort has been expended with limited success to minimize the differing embodiments of such shim elements required to fit numerous vehicle models and to provide fine and accurate correction of a wide range of misalignment conditions. Also, emphasis has been placed at simplifying both selection of the appropriate corrective taper and actual installation of the tapered shim element under confined and difficult circumstances.
Such tapered shim elements are employed in two fundamentally differing but related vehicle structures, i.e. at a steerable front wheel, and at a fixed rear wheel. When used at a steerable wheel, the tapered shim element can be rotated around the wheel axis when adjusting camber such that the taper is orthogonally resolved into camber and toe components. When the appropriate camber correction is realized, the toe component can be easily accommodated by the toe correction mechanism provided at steerable wheels, i.e. tie rod length adjustment. However, at fixed rear wheels the toe and camber must both be set by selecting a tapered shim element of just the proper taper, and resolving the camber and toe components to precisely correct both of the alignment settings. In practice this means the shim element must have a single proper taper, and that such taper must be properly oriented relative to toe and camber. Otherwise, two independent shim elements may be needed and stacked with the taper of one shim element oriented to correct toe and with the taper of the other oriented to correct camber.
U.S. Pat. Nos. 4,037,680 and 4,195,862 describe tapered shim elements adapted to correct the camber of driven, steerable wheels. Each describes a selection of tapered shim elements from which a choice can be made to correct wheel camber. The latter patent discusses color coded, filled polymer shim elements which seal when stacked with the taper axis (that which extends from the thin to the thick end of the shim element) in a vertical alignment.
U.S. Pat. No. 4,684,150 describes a set of twelve shim elements, each of a different taper, which have a series of notches at the periphery thereof. By selecting a shim element of an appropriate taper, and by positioning the shim element with the appropriate vertical orientation, both camber and toe can be corrected. The open notches allow the shim element to be repositioned without complete removal of the wheel mount. For greater correction, the shim elements can be stacked.
U.S. Pat. No. 4,872,699 discloses a set of shim elements of differing tapers having a series of frangible tabs around the periphery thereof. By breaking out selected tabs the shim elements can be configured to fit bolt patterns with differing vertical orientations of the shim elements. A comprehensive template system for determining breakout patterns is presented.
Ingalls Alignment Products has marketed a set of "808 Shims" consisting of two identical one and one-half degree tapered shim elements for use with fixed rear wheels. For corrections requiring other than a single one and one-half degree shim element, two individual shim elements are installed stacked in accord with a chart utilizing numerical markings imprinted in each shim element.
U.S. Pat. No. 774,042 discusses an early attempt to use two independent tapered members to correct alignment. However, no means for correlating measured misalignment and tapered member setting are suggested. Thus the concept, which appears to rely on eyeball corrections, would not be appropriate for modern vehicles.